Mitochondria are membrane-enclosed organelles distributed through the cytosol of most eukaryotic cells. Mitochondria are especially concentrated in myocardial tissue.
Complex 1 (“MC-1”) is a membrane-bound protein complex of 46 dissimilar subunits. This enzyme complex is one of three energy-transducing complexes that constitute the respiratory chain in mammalian mitochondria. This NADH-ubiquinone oxidoreductase is the point of entry for the majority of electrons that traverse the respiratory chain, eventually resulting in the reduction of oxygen to water (Q. Rev. Biophys. 1992, 25, 253-324). Examples of inhibitors of MC-1 include deguelin, piericidin A, ubicidin-3, rolliniastatin-1, rolliniastatin-2 (bullatacin), capsaicin, pyridaben, fenpyroximate, amytal, MPP+, quinolines, and quinolones (BBA 1998, 1364, 222-235). Studies have shown that interrupting the normal function of mitochondria could advantageously concentrate certain compounds in the mitochondria, and hence in the mitochondria-rich myocardial tissue. Compounds that include an imaging moiety (e.g., 18F) can be useful in determining such a build-up of compounds, thereby providing valuable diagnostic markers for myocardial perfusion imaging. In addition, such compounds may find application for the diagnosis of coronary artery disease (CAD).
CAD is a major cause of death in modern industrialized countries and it has been found previously that assessments of regional myocardial perfusion at rest and during stress (exercise or pharmacologic coronary vasodilation) are valuable for noninvasive diagnosis of CAD. While myocardial perfusion imaging (MPI) with Positron Emission Tomography (PET) has been shown to be superior in some embodiments as compared to single photon emission computed tomography (SPECT), widespread clinical use of PET MPI has been limited by the previously available PET myocardial perfusion tracers.
Several PET blood flow tracers, such as rubidium-82 (82Rb) chloride, nitrogen-13 (13N) ammonia, and oxygen-15 (15O) water, have been developed and validated for assessment of myocardial perfusion. 13N and 15O are cyclotron-produced isotopes with short half-lives. Therefore, their use is limited to facilities with an on-site cyclotron. Although 82Rb is a generator-produced tracer, its short half-life, the high cost of the generator, and the inability to perform studies in conjunction with treadmill exercise have made this tracer impractical for widespread use. Tracers that comprise 18F have, however, found potential application as imaging agents.
While current methods for preparing compounds comprising an imaging moiety include [18F]-fluorination chemistry, many methods focus on nucleophilic [18F]-fluorination chemistry using potassium fluoride (KF). Characteristically, these methods generate the elemental fluoride source through anion exchange between, for example, potassium carbonate (K2CO3) and a cyclotron-produced [18F]-containing species, and often require addition of the aza-crown ether Kryptofix® 222 (4,7,13,16,21,24-hexaoxa-1,10-diazabicyclo[8.8.8]-hexacosane) to enhance reactivity. While suitable for production of clinical quantities, the moderate efficiency, demanding purification and complex implementation of such method may not be suitable for widespread commercial application.
Accordingly, improved methods, systems, and apparatuses are needed for the synthesis of imaging agents.